Method for making oriented polyethylene foam and foam produced thereby

Abstract

A method for making an oriented foam generally includes the steps of: a. blending molten polyethylene and a blowing agent to form a foamable mixture; b. producing a foam by extruding the mixture at a predetermined rate through a die and into a region of reduced pressure so that the blowing agent expands within the mixture; and c. orienting the foam by drawing the foam out of the die at a rate that is between 1 and 1.5 times greater than the predetermined rate at which the mixture is extruded.

What is claimed is:  
     
       1. A method for making an oriented foam, comprising the steps of: 
       a. blending molten polyethylene and a blowing agent to form a foamable mixture;  
       b. producing a foam by extruding said mixture at a predetermined rate through a die and into a region of reduced pressure so that said blowing agent expands within said mixture, said mixture being at a temperature ranging from about 0.5 to about 2° F. above the crystallization temperature of said mixture as it is extruded through said die; and  
       c. orienting said foam by drawing said foam out of said die at a rate that is between 1.1 and 1.45 times greater than said predetermined rate at which said mixture is extruded, whereby, said foam has less than 5% variation in thickness.  
     
     
       2. The method of claim  1 , wherein said polyethylene comprises at least one member selected from the group consisting of low density polyethylene, high density polyethylene, and ethylene/alpha-olefin copolymer. 
     
     
       3. The method of claim  2 , wherein said polyethylene comprises low density polyethylene. 
     
     
       4. The method of claim  1 , wherein said oriented foam is a foam sheet having a thickness ranging from about 0.5 to about 10 centimeters. 
     
     
       5. The method of claim  4 , wherein said foam sheet has a thickness dimension and has less than 5% variation said thickness dimension. 
     
     
       6. The method of claim  1 , wherein said oriented foam is a foam sheet having a width ranging from about 10 to about 125 centimeters. 
     
     
       7. The method of claim  1 , wherein said oriented foam has a density ranging from about 10 to about 160 kg/m 3 . 
     
     
       8. The method of claim  1 , wherein said foam is drawn from said die at a rate that is between 1.15 and 1.35 times greater than said predetermined rate. 
     
     
       9. The method of claim  1 , wherein said polyethylene has a density of less than about 0.921 g/cc. 
     
     
       10. The method of claim  1 , wherein said oriented foam has a flexural modulus greater than about 350 psi. 
     
     
       11. An oriented foam sheet produced by the method of claim  1 .